The Colorado River — a major source of water for San Diego County — is the nation’s most endangered river, the conservation group American Rivers said in a Wednesday report.

“Flowing 1,400 miles across seven states, the Colorado River is truly a lifeline in the desert,” Bob Irvin, the organization’s president, said in a teleconference. “The river is so dammed and diverted that it dries to a trickle before the sea.”

The group issues an annual list of the most vulnerable waterways after looking at the rivers’ significance to communities and nature, the threats they face and the possibility for protective action.

The Colorado has made the list seven times and topped it three times, Irvin said. It provides drinking water for 36 million people, irrigates nearly 4 million acres of land, is home to numerous endangered species and supports a $26 billion recreation economy, American Rivers said.

It’s also threatened by overuse and outdated dams, the group said. Demand for Colorado River water has risen sharply during recent decades and is projected to continue escalating along with population growth. At the same time, the Southwest is expected to become drier and hotter.

Conservation measures that could help the Colorado include lining irrigation ditches, reusing treated wastewater for irrigation and improving plumbing efficiency in homes, Irvin said. His group also called on legislators to support WaterSmart, a federal program aimed at addressing water-supply sustainability in the Colorado River Basin.

The other endangered rivers named this year were the Flint in Georgia; the San Saba in Texas; the Little Plover in Wisconsin; the Catawba in North and South Carolina; the Boundary Waters in Minnesota; the Black Warrior in Alabama; the Rough & Ready and Baldface Creeks in Oregon; the Kootenai in British Columbia, Montana, and Idaho; and the Niobrara in Nebraska, South Dakota and Wyoming.